Rotational coupling device with wear compensation structure

ABSTRACT

A rotational coupling device for use as a clutch, a brake, or a combination clutch and brake is provided having structure to compensate for wear on braking surfaces. The device includes an armature coupled to an output member and movable between positions of engagement with a rotor and a brake plate. The brake plate is coupled to a stationary field shell that houses a conductor on one side of the rotor opposite the armature and brake plate. The brake plate is axially spaced from the field shell and a removable shim or adjustable spacer is disposed between the brake plate and the field shell. Removal of the shim or adjustment of the spacer permit movement of the brake plate towards the field shell to compensate for wear in any of the clutch or brake engagement surfaces of the device.

This application is a divisional application of, and claims priority to,U.S. patent application Ser. No. 12/268,739 filed Nov. 11, 2008, nowU.S. Pat. No. 8,123,012 the entire disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to rotational coupling devices such as brakes andclutches and, in particular, to a rotational coupling device havingstructure to compensate for wear on the braking surfaces of the device.

2. Discussion of Related Art

Rotational coupling devices such as clutches and brakes are used tocontrol transfer of torque between rotational bodies. One type ofconventional device is illustrated in U.S. Pat. Nos. 5,119,918,5,285,882 and 5,971,121, the entire disclosures of which areincorporated herein by reference. This device includes a rotor that iscoupled to an input shaft for rotation with the input shaft about arotational axis. A field shell is also disposed about the input shaft onone side of the rotor and is fixed against rotation. The field shelldefines radially spaced, axially extending inner and outer poles betweenwhich an electrical conductor is disposed, facing the rotor. A brakeplate is coupled to the field shell and axially spaced from the fieldshell. The brake plate is disposed on a side of the rotor opposite theconductor. An armature coupled to an output member is disposed on thesame side of the rotor as the brake plate and is disposed axiallybetween the rotor and the brake plate. The armature is coupled to anoutput member by a plurality of leaf springs. Energizing the conductorproduces a magnetic circuit in the field shell, rotor and armature thatdraws the armature into engagement with the rotor and couples the inputshaft and output member together for rotation. Upon deenergization ofthe conductor, the leaf springs draw the armature out of engagement withthe rotor and into engagement with the brake plate to brake the armatureand output member. Permanent magnets coupled to the brake plate are alsoused to create another magnetic circuit between the brake plate, thefield shell and the armature to assist the leaf springs in braking thearmature and output member.

Repeated engagement of the armature with the rotor during clutchengagement and with the brake plate during braking causes wear on theengagement surfaces of the armature, the rotor, and the brake plate.Over time, this wear increases the air gap that exists between thearmature and the rotor when the armature is engaged with the brakeplate. The increasing air gap requires increased current to draw thearmature into engagement with the rotor and engage the clutch. Thecurrent demand ultimately exceeds the service constraints of the devicethereby reducing the useful life of the device.

The inventor herein has recognized a need for a rotational couplingdevice that will minimize and/or eliminate one or more of theabove-identified deficiencies.

SUMMARY OF THE INVENTION

The present invention provides a rotational coupling device.

A rotational coupling device in accordance with one embodiment of thepresent invention includes a rotor coupled to an input shaft forrotation therewith. The input shaft is disposed about a rotational axisand the rotor defines a first clutch engagement surface. A field shellis disposed about the input shaft and fixed against rotation. Anelectrical conductor is disposed within the field shell on a first sideof the rotor. A brake plate is spaced axially from and coupled to thefield shell. The brake plate defines a first brake engagement surface.An armature is disposed axially between the rotor and the brake plate ona second side of the rotor opposite the conductor. The armature iscoupled to an output member and defines a second clutch engagementsurface and a second brake engagement surface. A permanent magnet iscoupled to one of the brake plate and the armature, the magnet urgingthe armature into engagement with the brake plate. A removable shim isdisposed axially between the brake plate and the field shell and atleast a portion of the shim has an axial dimension configured toapproximate an anticipated decrease in axial dimension in at least oneof the rotor, the armature and the brake plate resulting from wearduring engagement of the first and second clutch engagement surfaces andengagement of the first and second brake engagement surfaces.

A rotational coupling device in accordance with another embodiment ofthe present invention includes a rotor coupled to an input shaft forrotation therewith. The input shaft is disposed about a rotational axisand the rotor defines a first clutch engagement surface. A field shellis disposed about the input shaft and fixed against rotation. Anelectrical conductor is disposed within the field shell on a first sideof the rotor. A brake plate is spaced axially from and coupled to thefield shell. The brake plate defines a first brake engagement surface.An armature is disposed axially between the rotor and the brake plate ona second side of the rotor opposite the conductor. The armature iscoupled to an output member and defines a second clutch engagementsurface and a second brake engagement surface. A permanent magnet iscoupled to one of the brake plate and the armature, the magnet urgingthe armature into engagement with the brake plate. An adjustable spaceris disposed between the brake plate and the field shell. Adjustment ofthe spacer permits movement of the brake plate towards the field shellto compensate for wear on at least one of the first clutch engagementsurface, the second clutch engagement surface, the first brakeengagement surface and the second brake engagement surface. Theadjustable spacer may comprise, for example, a compressible member, adeformable member or a threaded bushing.

A rotational coupling device in accordance with the present inventionrepresents an improvement over conventional devices. The removable shimor adjustable spacer enables the brake plate to be moved axiallyrelative to the armature to compensate for wear on the engagementsurfaces of the rotor, armature, and brake plate. As a result, arelatively consistent air gap and magnetic circuit can be maintainedbetween the armature and the rotor so that the current required toengage the clutch does not increase beyond system constraints and theservice life of the device is extended.

These and other advantages of this invention will become apparent to oneskilled in the art from the following detailed description and theaccompanying drawings illustrating features of this invention by way ofexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a rotational coupling devicein accordance with one embodiment of the present invention.

FIG. 2 is a plan view of a removable shim used in the rotationalcoupling device of FIG. 1.

FIG. 3 is a partial cross-sectional view of a rotational coupling devicein accordance with another embodiment of the present invention.

FIG. 4 is a partial cross-sectional view of a rotational coupling devicein accordance with another embodiment of the present invention.

FIG. 5 is a partial cross-sectional view of a rotational coupling devicein accordance with another embodiment of the present invention.

FIGS. 6-7 are plan views of a portion of the coupling device shown inFIG. 5.

FIG. 8 is a partial cross-sectional view of a rotational coupling devicein accordance with another embodiment of the present invention.

FIGS. 9-10 are plan views of a portion of the coupling device shown inFIG. 8.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIG. 1illustrates a rotational coupling device 20 in accordance with oneembodiment of the present invention. Device 20 functions as a clutch toselectively transfer torque from an input shaft 22 to an output member24. Device 20 also functions as a brake on output member 24 when torqueis not being transferred to output member 24. Device 20 may be providedfor use in a riding lawnmower or similar device. It will be understoodby those of ordinary skill in the art, however, that device 20 may beused in a wide variety of applications requiring a clutch or brake.Device 20 may include a rotor 26, a key 28, a spacer 30, a field shell32, an electrical conduction assembly 34, an armature 36, a brake plate38, one or more permanent magnets 40 and a removable shim 42.

Input shaft 22 provides a source of torque for driving output member 24.Shaft 22 may be made from conventional metals and metal alloys and maybe solid or tubular. Shaft 22 is centered about a rotational axis 44 andis driven by an engine, electric motor or other conventional powersource. In the illustrated embodiment input shaft 22 is inserted intodevice 20 on a side of device 20 opposite output member 24. It should beunderstood, however, that the orientation of input shaft 22 and spacer30 could be reversed such that input shaft 22 is inserted into device 20on the same side as output member 24. Shaft 22 defines an axiallyextending keyway 46 configured to receive key 28.

Output member 24 transfers torque to a driven device such as a lawnmowerblade. Member 24 may comprise a conventional pulley around which atorque transmitting belt is wound and coupled to the driven device.

Rotor 26 is provided for selective engagement with armature 36 totransmit torque between input shaft 22 and output member 24. Rotor 26 isdisposed about axis 44 and is coupled to input shaft 22 for rotationtherewith. Rotor 26 may be made from conventional metals and metalalloys and includes a hub 48 and a rotor disc 50.

Hub 48 is tubular and defines a central bore into which input shaft 22extends. Hub 48 defines an axially extending keyway 52 shapedcomplementary to, and configured to receive, key 28. Keyway 52 isopposed to keyway 46 of shaft 22 upon assembly of device 20 on shaft 22.At either axial end, hub 48 abuts against and supports bearings 54, 56.At its radially outer diameter, hub 48 defines an axially extendinginner rotor pole 58. Hub 48 further defines an axially extending recess60 radially inwardly of pole 58 for a purpose described hereinbelow.

Disc 50 extends radially outwardly from hub 48. Disc 50 is coupled tohub 48 through, for example, a press-fit relationship includingplurality of complementary lugs and notches. As is known in the art,disc 50 may include a plurality of radially spaced rows of angularlyspaced, banana shaped slots 62. Upon energization of conduction assembly34, slots 62 cause magnetic flux to travel back and forth between disc50 and armature 36 across an air gap enabling a high torque engagementbetween rotor 26 and armature 36. In the illustrated embodiment, disc 50includes three rows of slots 62. It should be understood, however, thatthe number of rows of slots 62 the number of slots 62 in any one row,and the size and shape of slots 62 may vary. At its outer diameter, disc50 defines an axially extending outer rotor pole 64. Pole 64 is radiallyaligned with pole 58 and spaced radially outwardly of pole 58.

Key 28 is provided to rotatably couple shaft 22 and rotor 26. Key 28 maybe made from conventional metals and metal alloys. Kay 28 is configuredto be received within opposed keyways 46, 52 of shaft 22 and rotor hub48, respectively. Key 28 may be generally square or rectangular incross-section. Key 28 and keyway 52 may be shaped complementary to oneanother in such a way that radially inward movement of key 28 relativeto rotor 26 after installation of key 28 in keyway 52 is limited. Forexample, key 28 may assume a substantially keystone shape in radialcross-section and taper moving radially inwardly from its radiallyoutermost edge. Key 28 may also be shaped complementary to spacer 30.Key 28 may have a chamfered or beveled edge 66 at either end to enableeasier assembly.

Spacer 30 is provided to support output member 24 in assembled relationwith the other components of device 20 and may be made from conventionalmaterials including powdered metals. Spacer 30 is disposed about axis 44and is generally cylindrical in shape. Spacer 30 is configured toreceive a fastener (not shown) that extends through spacer 30 and intoinput shaft 22. Spacer 30 may define a head 68 at one axial end having aplurality of flats 70 that allow input shaft 22 to be secured whileapplying torque to the fastener. Spacer 30 may further define a body 72extending axially from head 68. Body 72 has a generally cylindricalouter surface 74 on which bearing 56 may be supported between opposedshoulders on rotor hub 48 and spacer 30. Spacer 30 may be shaped in acomplementary fashion relative to key 28 to limit radial and axialmovement of key 28 relative to spacer 30. Spacer 30 may define anaxially extending recess 76 closed at one axial end and configured toreceive one end of key 28. Upon assembly of device 20, radially inwardand outward movement of key 28 is limited relative to spacer 30 andaxial movement of key 28 relative to spacer 30 is also limited in oneaxial direction (to the right in FIG. 1). It should be understood thatthe key 28 and spacer 30 could be shaped in a number of ways providedthat key 28 and spacer 30 are shaped in a complementary fashion to limitradial and/or axial movement of key 28 relative to spacer 30.

Field shell 32 is provided to house conduction assembly 34. Shell 32also forms part of a magnetic circuit that causes the selectiveengagement of rotor 26 and armature 36. Field shell 32 may be made fromconventional metals and metal alloys, including steel. Shell 32 iscylindrical and is disposed about axis 44 and is supported on an outerrace of bearing 54. Shell 32 is fixed against rotation through, forexample, a fastener (not shown) extending through a slot (not shown) inshell 32. Shell 32 is generally U-shaped in cross-section and includesradially inner and radially outer annular members 78, 80.

Inner member 78 is supported on an outer race of bearing 54. Member 78is generally L-shaped in cross-section and defines an axially extendinginner pole 82. Pole 82 extends into recess 60 of hub 48 of rotor 26 andis therefore disposed radially inwardly of inner rotor pole 58. Asdescribed more fully in commonly assigned and copending U.S. patentapplication Ser. No. 11/150,671, the entire disclosure of which isincorporated herein by reference, the relative location of poles 58, 82is advantageous for several reasons. First, the magnetic efficiency ofthe magnetic circuit involving rotor 26, field shell 32 and armature 36is improved by reducing the number of air gaps for at least some of themagnetic flux in the circuit. Second, the annular gap in whichconduction assembly 34 is disposed is enlarged enabling easier insertionand fastening of assembly 34 within field shell 32.

Outer member 80 is coupled to and supported on inner member 78. Outermember 80 defines an end wall 84, an axially extending outer pole 86,and a flange 88. End wall 84 extends radially outwardly from member 78.Pole 86 is integral with, and extends axially from, end wall 84. Pole 86is disposed radially outwardly of pole 64 of rotor 26. Flange 88 isintegral with, and extends radially outwardly from, pole 86 at an end ofpole 86 opposite end wall 84. Flange 88 extends along at least a portionof the circumference of pole 86.

Conduction assembly 34 is provided to create a magnetic circuit amongrotor 26, field shell 32, and armature 36 to cause movement of armature36 into engagement with rotor 26 and transmission of torque from inputshaft 22 to output member 24. Conduction assembly 34 is generallyannular and is disposed about axis 44 within field shell 32. Inparticular, assembly 34 is disposed between the inner and outer poles82, 86 of shell 32. Assembly 34 includes a conductor 90 and a shell 92.

Conductor 90 may comprise a conventional copper coil although otherknown conductors may alternatively be used. Conductor 90 may beconnected electrically to a power supply (not shown) such as a battery.Upon energization of conductor 90, a magnetic circuit is formed betweenrotor 26, field shell 32, and armature 36. Magnetic flux flows fromouter pole 86 of shell 32 across an air gap to outer pole 64 of rotor26. Flux then travels back and forth between disc 50 and armature 36across the air gap between them. Flux then flows from disc 50 of rotor26 to hub 48 of rotor 26. Finally, flux flows from hub 48 back tomembers 78, 80 of field shell 32 along several paths. In particular, aportion of the flux flows directly from inner rotor pole 58 to member80. Another portion of the flux flows from hub 48 through inner pole 82of member 78 before flowing to member 80. Still another portion of theflux may flow from hub 48 to a support hub 94 radially inwardly ofbearing 54 and then to member 78 and member 80 allowing a portion of theflux to avoid the high density area of inner rotor pole 58 and innerfield shell pole 82 and further improving the magnetic efficiency of thecircuit.

Shell 92 is provided to house conductor 90 and is also used to mountconductor 90 within field shell 32. Shell 92 may be molded fromconventional plastics. Shell 92 may include an integral terminalconnector 96 through which conductor 90 may be electrically connected toa power source. Shell 92 may also define one or more lugs (not shown)sized to be received within recesses in end wall 84 of field shell 32 toprevent rotation of conduction assembly 34. Shell 92 may include aradially outwardly extending flange (not shown) disposed proximate outerpole 86 of field shell 32 and affixed to shell 32 at a plurality ofpoints as described in commonly assigned pending U.S. patent applicationSer. No. 11/150,670, the entire disclosure of which is incorporatedherein by reference.

Armature 36 is provided to transmit a braking torque to output member 24and to selectively transmit a drive torque from rotor 26 to outputmember 24. Armature 36 may be made form a variety of conventional metalsand metal alloys including steel. Armature 36 is annular in constructionand disposed about axis 44. Armature 36 is axially spaced from rotor 26by an air gap. Like rotor disc 50, armature 36 includes a plurality ofradially spaced rows of angularly spaced slots 98 that facilitate travelof magnetic flux back and forth between rotor 26 and armature 36 uponenergization of conduction assembly 34. In the illustrated embodiment,armature 36 includes two rows of slots 98. It should be understood thatthe number of rows of slots 98 on armature 36, the number of slots 98 inany one row, and the size and shape of slots 98 may vary. Armature 36 iscoupled to output member 24. In particular, armature 36 may be coupledto output member 24 by a plurality of leaf springs 100. Springs 100transmit drive and braking torque from armature 36 to output member 24and allow for axial movement of armature 36 relative to member 24 andtowards and away from rotor disc 50. Springs 100 may be made fromstainless steel and are connected at one end to armature 36 and at anopposite end to output member 24 using conventional fasteners 102 suchas rivets, screws, bolts, or pins.

Brake plate 38 provides a braking surface for engagement by armature 36to brake output member 24. Plate 38 further forms part of a magneticcircuit with armature 36 and magnets 40 and may provide a means forhousing magnet 40. Brake plate 38 may be made from conventionalmaterials having a relatively low magnetic reluctance includingconventional metals and metal alloys such as steel. Brake plate 38extends about at least a portion of the circumference of device 20, andpreferably only a portion of the circumference of device 20, and iscoupled to field shell 32. In particular, brake plate 38 is coupled toflange 88 of field shell 32 and suspended therefrom using one or morefasteners 104. Fasteners 104 may be made from a material or materialshaving a relatively high magnetic reluctance (including non-magneticmaterials) to reduce or eliminate flux transfer between brake plate 38and field shell 32 and thereby facilitate clutch engagement whenconduction assembly 34 is energized. Throughout this application, theterm “relatively high magnetic reluctance” shall mean a magneticreluctance that is greater than the magnetic reluctance of armature 36such that flux transfer is more likely to occur between brake plate 38and armature 36 than between brake plate 38 and fastener 104. Brakeplate 38 may be axially spaced from flange 88 of field shell 32 usingone or more spacers 106. Spacers 106 may include bores 108 through whichfasteners 104 extend. Spacers 106 may likewise be made from a materialor materials having a relatively high magnetic reluctance (includingnon-magnetic materials) to reduce or eliminate flux transfer betweenbrake plate 38 and field shell 32.

Magnets 40 are provided to create a magnetic circuit between brake plate38 and armature 36 to draw armature 36 into engagement with brake plate38 and provide a braking torque to output member 24. Magnets 40 maycomprise neodymium iron boron (Nd—Fe—B) magnets or other known permanentmagnets. Magnets 40 preferably are disposed about only a portion of thecircumference of device 20. Magnets 40 are axially aligned with aportion of armature 36 thereby reducing the number of air gaps in themagnetic circuit relative to conventional coupling devices and improvingmagnetic efficiency, as described in greater detail in commonlyassigned, copending U.S. patent application Ser. No. 11/150,027, theentire disclosure of which is incorporated herein by reference. Magnets40 may be oriented such that magnetic flux travels throughout magnets 40in an axial, radial, or arcuate (circumferential) direction. Magnets 40may be received within pockets 110 formed in brake plate 38.Alternatively, magnets 40 may instead be received within a pocket formedin armature 36 and axially aligned with brake plate 38. Magnets 40 maybe arranged such that one face of each magnet 40 is flush with one side(and the braking surface) of brake plate 38 (or armature 36). By placingmagnets 40 such that one face is flush with the braking surface of brakeplate 38 (or armature 36), magnets 40 add to the wear surface of brakeplate 38 (or armature 36) increasing its wear resistance and the brakingsurface.

Shim 42 is provided to allow for adjustment of the position of brakeplate 38 to compensate for wear on the clutch engagement surfaces 112,114 of rotor 26 and armature 36, respectively and on the brakeengagement surfaces 116, 118 of armature 36 and brake 38, respectively.Shim 42 may be made from a variety of materials including conventionalmetals and metal alloys. Shim 42 is disposed axially between field shell32 and brake plate 38 with spacer 106. In the illustrated embodiment,shim 42 is disposed axially between field shell 32 and spacer 106 and isnearer to field shell 32 than brake plate 38, but it should beunderstood that the positions of shim 42 and spacer 106 could bereversed. Shim 42 may be in contact with brake plate 38.

Referring to FIG. 2, shim 42 has radially inner and outer edges 120,122. Shim 42 defines a pair of slots 124 formed in inner edge 120 thatis configured to receive fasteners 104. Slots 124 have a shape that iscomplementary to the shape of fasteners 104. In the illustratedembodiment, each slot 124 is substantially U-shaped and configured toreceive a circular fastener. The depth d₁ of each slot 124 may begreater than the diameter of a corresponding fastener 104 such that aportion of shim 42 (such as any of legs 126, 127, 128) is disposedfurther radially inward than fastener 104 (best shown in FIG. 1).

Referring again to FIG. 1, at least a portion of shim 42 (i.e., theportion between field shell 32 and spacer 106) has an axial dimension d₂that is configured to approximate an anticipated decrease in axialdimension of one or more of rotor 26, armature 36 and brake plate 38resulting from wear during engagement of clutch engagement surfaces 112,114 and brake engagement surfaces 116, 118. For example, dimension d₂may be chosen to approximate a decrease in axial dimension d₃ inarmature 36 and brake plate 38 resulting from wear during engagement ofarmature 36 and brake plate 38. During operation of device 20, theclutch engagement surfaces 112, 114 and brake engagement surfaces 116,118 begin to wear. As a result, the air gap that exists between rotor 26and armature 36 when armature 36 is engaged with brake plate 38increases. The increased air gap requires an increase in current inconduction assembly 34 to strengthen the magnetic circuit between rotor26 and armature 36 and continue to draw armature 36 into engagement withrotor 26. Eventually, the increasing current demand would exceed servicelimitations on device 20, thereby limiting the useful life of device 20.Because shim 42 has an axial dimension d₂ chosen to approximate adecrease in axial dimension in one or more of rotor 26, armature 36 andbrake plate 38 (e.g., a decrease d₃ in the axial dimensions (or brakeengagement surfaces 116, 118) of armature 36 and brake plate 38), shim42 can be removed at a predetermined time in the service life of device20 and/or when inspection of device 20 reveals that wear on rotor 26,armature 36 and/or brake plate 38 has made removal appropriate. Uponremoval of shim 42, brake plate 38 may be moved towards flange 88 offield shell 32. This action will substantially restore the original airgap between rotor 26 and armature 36 by compensating for wear on brakingsurfaces 116, 118 of armature 36 and brake plate 38 and on clutchengagement surfaces 112, 114 of rotor 26 and armature 36 that wouldotherwise cause armature 36 to be located further from rotor 26 whenengaged with brake plate 38. By maintaining the air gap, increasedcurrent demands during clutch engagement can be minimized and theservice life of device 10 extended.

The radially outer portion of shim 42 may define an axially ending lip130. As shown in FIG. 1, lip 130 has an axial dimension d₄ that isgreater than dimension d₂. Lip 130 facilitates removal of shim 42 byhand or tool by providing a surface 132 against which a force can beapplied to move shim 42 radially outwardly away from device 20.

Referring now to FIG. 3, a rotational coupling device 134 in accordancewith another embodiment of the present invention is illustrated. Device134 is similar to device 20. Therefore, like structures are identifiedwith the same reference numbers and a description of like structures maybe found hereinabove. Device 134 differs from device 20 in that device134 includes a adjustable spacer 136. As used herein, “adjustable”refers to adjustment of the position or form of the spacer within therotational coupling device and excludes simply removing the spacer (or apart of the spacer) from the device.

Spacer 136 is provided to allow brake plate 38 to be moved axiallytowards armature 36 to compensate for wear on one or more of clutchengagement surfaces 112, 114 and brake engagement surfaces 116, 118.Spacer 136 may comprise a bushing that is disposed between flange 88 offield shell 32 and brake plate 38 and extends through flange 88. Oneaxial end 138 of spacer 136 abuts brake plate 38. The opposite axial end140 of spacer 136 may define a head 142. The radially outer surface ofspacer 136 defines a plurality of threads configured to engagecorresponding threads in an aperture 144 in flange 88. Rotation ofspacer 136 causes movement of spacer 136 parallel to axis 44 and allowscorresponding movement of brake plate 38 thereby permitting infiniteadjustment of the axial position of brake plate 38. Spacer 136 defines abore 146 configured to receive fastener 104. Fastener 104 extendsthrough aligned bores in flange 88, spacer 136 and brake plate 38 tosecure the position of brake plate 38 against end 138 of spacer 136.Spacer 136 may be made from a material or materials having a relativelyhigh magnetic reluctance (including non-magnetic materials) to reduce oreliminate flux transfer between brake plate 38 and field shell 32.

Referring now to FIG. 4, a rotational coupling device 148 in accordancewith another embodiment of the present invention is illustrated. Device148 is again similar to device 20. Therefore, like structures areidentified with the same reference numbers and a description of likestructures may be found hereinabove. Device 148 differs from device 20in that device 148 includes a adjustable spacer 150.

Spacer 150 is again provided to allow brake plate 38 to be moved axiallytowards armature 36 to compensate for wear on one or more of clutchengagement surfaces 112, 114 and brake engagement surfaces 116, 118.Spacer 150 may comprise a compressible or crushable body that isdisposed between flange 88 of field shell 32 and brake plate 38. Oneaxial end 152 of spacer 150 abuts brake plate 38 while the oppositeaxial end 154 of spacer 150 abuts flange 88 of field shell 32. Spacer150 defines a bore 156 configured to receive fastener 104. Fastener 104extends through aligned bores in flange 88, spacer 150 and brake plate38. Rotation of fastener 104 draws brake plate 38 towards flange 88 andcompresses spacer 150 thereby permitting infinite adjustment of theaxial position of brake plate 38. Spacer 150 may again be made from amaterial or materials having a relatively high magnetic reluctance(including non-magnetic materials) to reduce or eliminate flux transferbetween brake plate 38 and field shell 32.

Referring now to FIGS. 5-7, a rotational coupling device 158 inaccordance with another embodiment of the present invention isillustrated. Device 158 is again similar to device 20. Therefore, likestructures are identified with the same reference numbers and adescription of like structures may be found hereinabove. Device 158differs from device 20 in that device 158 includes a adjustable spacer160.

Spacer 160 is again provided to allow brake plate 38 to be moved axiallytowards armature 36 to compensate for wear on one or more of clutchengagement surfaces 112, 114 and brake engagement surfaces 116, 118.Spacer 160 may comprise a deformable body that is disposed betweenflange 88 of field shell 32 and brake plate 38. In particular, spacer160 may comprise an elastically deformable body. As shown in theillustrated embodiment, spacer 160 may form a unitary structure withbrake plate 38. It should be understood, however, that spacer 160 mayform a separate component. Spacer 160 extends axially relative to brakeplate 38 such that spacer 160 is disposed nearer to flange 88 thanengagement surface 118 of brake plate 38. Referring to FIG. 6, in theillustrated embodiment, spacer 160 is connected to brake plate 38 at aneck 162. Arms 164, 166 extend axially and circumferentially from eitherside of neck 162. Arms 164, 166 include semicircular ends definingrecesses 168, 170, respectively, having an inner diameter about equal insize to an outer diameter of corresponding bosses 172, 174 formed inbrake plate 38 through which fasteners 104 extend. Rotation of fasteners104 draws brake plate 38 towards flange 88 and deforms arms 164, 166urging them towards brake plate 38 thereby permitting infiniteadjustment of the axial position of brake plate 38. Device 158 mayfurther include washers 176 disposed about fasteners 104 between arms164, 166 of spacer 160 and flange 88. Washers 176 may be made from amaterial or materials having a relatively high magnetic reluctance(including non-magnetic materials) to reduce or eliminate flux transferbetween brake plate 38 and field shell 32.

Referring now to FIGS. 8-10, a rotational coupling device 178 inaccordance with another embodiment of the present invention isillustrated. Device 178 is again similar to device 20. Therefore, likestructures are identified with the same reference numbers and adescription of like structures may be found hereinabove. Device 178differs from device 20 in that device 178 includes a adjustable spacer180.

Spacer 180 is again provided to allow brake plate 38 to be moved axiallytowards armature 36 to compensate for wear on one or more of clutchengagement surfaces 112, 114 and brake engagement surfaces 116, 118.Spacer 180 comprises a body that is in frictional engagement with brakeplate 38. Spacer 180 may be formed from the same stamping as brake plate38 through a semi-pierce operation. Spacer 180 is formed in such a waythat spacer 180 can be placed in a tight frictional engagement withbrake plate 38. In the illustrated embodiment, spacer 180 definessemicircular ends defining recesses 182, 184, respectively, having aninner diameter about equal in size to an outer diameter of correspondingbosses 172, 174 formed in brake plate 38 through which fasteners 104extend. As compared to the spacer 160 shown in FIGS. 5-7, however,spacer 180 always radially overlaps at least a portion of brake plate 38as shown in FIG. 8. Rotation of fasteners 104 draws brake plate 38towards flange 88 against the frictional forces between spacer 180 andbrake plate 138 creating additional radial overlap between spacer 180and brake plate 38 and thereby permitting infinite adjustment of theaxial position of brake plate 38. This arrangement results in anincreasing radial (and ultimately frictional) force as rotation offastener 104 draws brake plate 38 towards flange 88 of field shell 32.

While the invention has been shown and described with reference to oneor more particular embodiments thereof, it will be understood by thoseof skill in the art that various changes and modifications can be madewithout departing from the spirit and scope of the invention. Forexample, it should be understood that although only one shim is shown inthe illustrated embodiment, a plurality of shims could be used tofacilitate finer compensation adjustments. It should also be understoodthat the shape of shim 42 could vary from the illustrated embodimentwithout departing from the spirit of the present invention.

1. A rotational coupling device, comprising: a rotor coupled to an inputshaft for rotation therewith, said input shaft disposed about arotational axis and said rotor defining a first clutch engagementsurface; a field shell disposed about said input shaft and fixed againstrotation; an electrical conductor disposed within said field shell on afirst side of said rotor; a brake plate spaced axially from and coupledto said field shell, said brake plate defining a first brake engagementsurface; an armature disposed axially between said rotor and said brakeplate on a second side of said rotor opposite said conductor, saidarmature coupled to an output member and defining a second clutchengagement surface facing and a second brake engagement surface; apermanent magnet coupled to one of said brake plate and said armature,said magnet urging said armature into engagement with said brake plate;and, an adjustable spacer disposed between said brake plate and saidfield shell, adjustment of said spacer permitting movement of said brakeplate towards said field shell to compensate for wear on at least one ofsaid first clutch engagement surface, said second clutch engagementsurface, said first brake engagement surface and said second brakeengagement surface wherein said adjustable spacer comprises acompressible body.
 2. The rotational coupling device of claim 1 whereinsaid compressible body is made from a material having a higher magneticreluctance than said field shell and said brake plate.
 3. The rotationalcoupling device of claim 1, further comprising a fastener extendingthrough aligned bores in said field shell, said compressible body andsaid brake plate.
 4. A rotational coupling device, comprising: a rotorcoupled to an input shaft for rotation therewith, said input shaftdisposed about a rotational axis and said rotor defining a first clutchengagement surface; a field shell disposed about said input shaft andfixed against rotation; an electrical conductor disposed within saidfield shell on a first side of said rotor; a brake plate spaced axiallyfrom and coupled to said field shell, said brake plate defining a firstbrake engagement surface; an armature disposed axially between saidrotor and said brake plate on a second side of said rotor opposite saidconductor, said armature coupled to an output member and defining asecond clutch engagement surface facing and a second brake engagementsurface; a permanent magnet coupled to one of said brake plate and saidarmature, said magnet urging said armature into engagement with saidbrake plate; and, an adjustable spacer disposed between said brake plateand said field shell, adjustment of said spacer permitting movement ofsaid brake plate towards said field shell to compensate for wear on atleast one of said first clutch engagement surface, said second clutchengagement surface, said first brake engagement surface and said secondbrake engagement surface wherein said adjustable spacer comprises adeformable body.
 5. The rotational coupling device of claim 4 whereinsaid brake plate and said deformable body form a unitary structure. 6.The rotational coupling device of claim 4 wherein said deformable bodyis elastically deformable.